Active vitamin D3 (1α,25-dihydroxyvitamin D3) is a hormone having various physiological effects, and it is suggested that active vitamin D3 can be widely used as a medicine for various diseases. For example, Rocaltrol™ having active vitamin D3 as an active ingredient is actually used as a therapeutic agent for hyperparathyroidism, osteoporosis and the like. On the other hand, it is well known that active vitamin D3 increases the blood calcium level and may cause hypercalcemia as a side effect. The dose of active vitamin D3 or the patients suitable for active vitamin D3 is limited because of this side effect of active vitamin D3, and useful and various physiological effects of active vitamin D3 are not fully utilized for therapy of diseases, actually.
Various active vitamin D3 derivatives are synthesized to solve this problem. This is an attempt of modifying the structure of active vitamin D3 to provide vitamin D3-like agonists with a strong and desirable effect among various physiological effects of active vitamin D3 and, on the other hand, with a small effect of increasing the blood calcium level as a side effect. In such an attempt, there have been recently reported mimic compounds (VD3 mimic), specifically, compounds not having a secosteroid skeleton that is a characteristic structure of active vitamin D3 but having a vitamin D3-like effect (WO 00/10958, WO 2004/063345 and WO 2005/037755).